Photographic emulsion



Patented May 23, 1939 UNITED STATES PATENT OFFICE PHOTOGRAPH() EMULSIONCharles E. K. Mees, Rochester, N. Y., assignor to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey 15 Claims.

This invention relates to sensitized photographic emulsions and moreparticularly to photographic emulsions, such as those of thegelatine-silverhalide type, containing a mixture or combination of twoor more sensitizing materials, at least one oi which cooperates with atleast one other to alter the sensitivity of the emulsion to a greaterdegree than is possible with any one of the sensitizing materials alone.The sensitization produced by my combination is always greater, in somespectral region, than the sum ltotal of the sensitizations produced bythe separate sensitizing materials. The sensitizing materials of mycombinations'are substances generally referred to as dyes and moreparticularly as dyes of the cyanine class.

It is known in the art of making photographic emulsions that certaindyes of the cyanine class alter the sensitivity of photographicemulsions of ,o the gelatino-silver-halide type, when incor-y poratedtherein. The sensitizing effect produced by the dye does not increaseproportionally to the amount of dye, but passes through a maximum as-the concentration lis increased. Within the range of concentrationsmost useful in practice, the sensitivity increases much more slowly thanthe concentration of the dye. Likewise, the

combined effect of two or more dyes on an emulsion is rarely equivalentto the sum of their separate eilects; in general it is much less. Mostcommonly, the combined eiect is no greater than the eiIect of a singleone of the dyes employed in a concentration equal to the sum of theconcentrations of all the dyes in the combination. Very frequently, thecombined effect of two dyes is less than that of one of them alone.

lI have found with certain combinations of two or more cyanlne dyes,that the combined sensitization is substantially greater, in somespectral o region, than that of any one of ,the dyes in the absence ofthe other or others. I will call this phenomenon supersensitization. Ingeneral, atleast one dye of my combination may be said to besupersensitized by the other or others. The

dye which is supersensitized may be called the basic sensitizer and theother dye the supersensitizer. However, the e'ect may be mutual and thedyes indistinguishable from the standpoint of which is supersensitized.

, Supersensitization is a highly specific phenomenon and is found onlyin mixtures or combinations of dyes from certain specic groups.Supersensitization can be most readily observed, when a dye issupersensitized in a. spectral region for which the other dye does notsensitize; for example, when the red sensitization produced by dye Aincreases in the presence of dye B which sensitizes only for the green.When two or more dyes sensitize for approximately the same or widelyoverlapping spectral regions (as in a number of the cases to bedescribed in the instant application) supersensitization can still bedetected, because if supersensitization obtains in such cases the totaloptical sensitization produced by a combination of two or more dyes willalways be greater, under favorable conditions, than that which can beproduced by any dye of the combination alone at any concentration. Themagnitude of the supersensitization depends upon the relative andabsolute concentrations of the dyes in the emulsion and on the type ofemulsion. By

suitable choice of conditions supersensitization can always be made toassume values which are readily observable.

In my copending application Serial No. 641,177,

l flledNovember 4, 1932, (now United States Patent No. 2,075,046, datedMarch 30, 1937), I have described emulsions containing supersensitizingcombinations of plnscyanol with dialkylaminostyryl derivatives of alkylquaternary salts of simple nitrogen-containing heterocyclic bases; in mycopending application Serial No. 641,178, led November 4, 1932, (nowUnited States PatentNo. 2,075,047, dated March 30, 1937), are describedemulsions containing supersensitizing combinations of sulfur orselenium-containing pseudocyanine dyes with styryl derivatives of alkylquaternary salts of simple nitrogen heterocyclic bases; and in mycopending application Serial No. 641,179, filed November 4, 1932, (nowUnited States Patent No. 2,075,048, dated March 30, 1937), are describedemulsions containing supersensitizing combinations of sulfur orseleniumcontaining carbocyanine dyes with 2,2dialkyl8-alkyl3,4,3,4'dibenzothiacarbocyanine dyes.

In my instant application, which is a division of my copendingapplication Serial No. 120,967, filed January 16, 1937, emulsionscontaining supersensitizing mixtures or combinations of one or moresensitizing dyes of the group of oxathiazolocarbocyanine dyes having analkyl substituent in at least one of the 4 and 5positions with one ormore sensitizing pseudocyanine dyes selected from the group consistingof 2,2-cyanine dyes,

binatins, although I do not intend to imply that A the dyes arechemically combined.

element comprising a support coated with such An object of my invention,therefore, is to provide photographic emulsions containing asupersensitizing combination of cyanine dyes. A further object is toprovide a' process for sensitizing photographic emulsions withsupersensitizing combinations of cyanirie dyes and to provide a methodof increasing the sensitivity of photographic emulsions sensitized withcyanine dyes. A still further object is to provide a 'photographicsupersensitized emulsions. Other more specific objects will becomeapparent upon a complete perusal of these specifications.

The dyes which I employ in my supersensitiz- A ing mixtures aresensitizers of photographic emulsions when used alone. While there ismore than one manner of formulating and naming the dyes which I employin practicing my invention, it is believed that the formulas, systems ofn` with those used during the development of the cyanine dye art to itspresent stage. The most probable formulae 1 of representative dye-typesare given below,l in order to clearly set forth the nature ofthematerials employed in my supersensitizing mixtures. These formulasshouldnot be construed as limiting my invention, except as indicated inthe appendedvclaims.

Among the oxathiazol'ocarbocyanine, dyes useful in practicing myinvention are the following: The 4-alkyloxathiazolocarbocyanines, whichcan be represented by the following general for- In the above formula, Rand Rf'represent. allwl groups4 and X .represents an acid radical. The

' alkyl groups of at least two carbon'atoms. The' dyes wherein R and Rrepresent ethyl are especially useful.

Oxathiazolocarbocyanine dyes can be prepared by reacting a2.-methylthiazole base with an equimolecular proportion of analkvl-p-toluenesulfonate, e. g.; ethyl-ptoluenesulfonate, by heating forlseveral hours' (advantageously-4 or 5 days) at about 95 to 100 C. Thecrude 'so-prepared Quaternary salt is'then reacted with a 1-l-acetanilidovinyl) -benzoxazole alkyl quaternary salt, e. g., theethiodide, by refiuxing in dry pyridine for about minutes or longer. Thecrude quatemary salt4 is advantageously employed in an excess of about20%. The quantity of pyridine is conveniently about 10 cc. for each gramof 2- methylthiazole base use'd. The pyridine reaction mixture isconcentrated by removing a portion of the pyridine under vacuum. Abouttwo liters of diethyl ether is then added to the residuum to umher# ingand names used herein are in accordance example as the chlorides,

form a solution from which the dye separates upon chilling afterstanding. 'Ihe dye can e re, crystallized from ,methyl alcohol afterwashing :with a little water and acetone.

Among the pseudocyanine dyes, which I employ in practicing my invention,are the following:

The 2,2'x-'cyanine dyes, which can be represented by the followinggeneral formula.:

The selena-2'cyanine dyes, which can be represented by the followinggeneral formula:

The benzothia-2cyanine dyes, which can be represented by the followinggeneral formula:

The oxazolo-2'cyanine dyes, whichA can be represented by the followinggeneral formula:

In all of the` above formulas of pseudocyanine dyes, R and R.' representalkyl groups and X represents an acid radical. In practicing myinvention, I have found it convenient to employ the pseudocyaninedye-iodides (wherein X represents iodine). However, other pseudocyaninesalts can be employed, such for example as the chlorides, bromides,perchlorates, alkylsulfates or alkyl-p-toluenesulfonates. I have furtherfound it advantageous to emploi7 pseudocyanine dyes wherein R and R-represent an alkyl group of from oneY to four'carbon atoms. The dyeswhere. in'R and R.' represent ethyl are particularly use4 .ful inpracticing my invention. The pseudocyanine dyes can be substituted intheir nuclei with imple substituents which dov not interfere with 1sensitizing' properties, such for example as alkyl, chloro, alkbxy orvamino groups. The oxazo1o-.2

cyanlnes can be substituted inthe i'lve position with? substituents suchas alkyl groups or aryl4 groups of the benzene series, for examplephenyl.

Brooker and Keyes in the J ournaQf the Ameri-` can' Chemical Society,vol. 57, pages 2488-2491 (1935) review the literature pertaining topseudocyanine dyes and describe a method for the p eparation thereof.40xazolo2cyanine dyes are described in U. S. Patent No. 1,969,446, datedAugust 7, 1934.

By way of illustration, I have found the following combinations of dyesto exhibit supersensiti'zing effects. These illustrations are notintended t0 limit my invention. y

' one or more of the following:

y nine salts, as exemplied by the dye-iodide, with one or more of thefollowing:

The oxathiazolocarbocyanine dyes can be substi-A tuted in thetrimethehyl chain with alkyl groups,

azolocarbocyanine dyes containing methyl groups on the nitrogen atoms,such as in the case of 2 ethyl 3',4'dimethyloxathiazolocarbocyaninesalts,v are generally, less satisfactoryin practicing my invention.However, as illustrated above, the oxathiazolocarbocyanine dyescontaining methyl groups on the nitrogen atoms can be combined with3,2cyanine dyes and 2,4-benzothia-2cya nine dyes in practicing myinvention. Among the oxazolo-2cyanines those substituted in the fourposition of the oxazole nucleus by an alkyl group, such as methyl, or anaryl group, such as phenyl for example, are especially useful inpracticing my invention.

In general, it can be s aid of my combinations that the pseudocyanine isthe dye supersensitized (basic sensitizer) and theoxathiazolocarbocyanine is the supersensitizer. In the combinations oi'2,1-diethyl--i-phenyloxazolo-2'cyanine with theoxathiazolocarbocyanines, it is apparently the former which is thesupersensitizer. However, the nature of this relationship between thedyes of my combination is frequently ldifficult to determine and is,- infact, immaterial to the practice of my invention.

While I have illustrated onlyv combinations containing two dyes, mycombinations can'as well contain one oxathiazolocarbocyaninelcooperating with two or more pseudocyanine dyes. Likewise, mycombinations can contain one pseudocyanine dye cooperating with two ormore oxathiazolocarbocyanine dyes.

The objects of my invention can be accomplished by merely incorporatingthe appropriate dyes in an ordinary photographic emulsion of ordinaryconcentration. My invention is particularly directed tothe ordinarilyemployed gelatinesilver-halide emulsions. However, my supersensitizingcombinations can be employed in emulsions in which the carrierv is otherthan gelatin, .for example, a resinous substance or cellulosicderivative which has substantially no deleterious effect on the lightsensitive materials. As'silver halide emulsionsI include such emulsionsas are commonly employed in the art, for example, silver chloride orsilver bromide emulsions which can contain other salts which may belight sensitive.

By way of illustration, the herein described super- -sensitizedemulsions were prepared employing an ordinary gelatine-silver-bromideemulsion of ordinary concentration (approximately 46 g. of silver halideper liter). -The dyes were generally employed'in Aconcentrations of theorder of 10 mgs. each per liter of'ordinary emulsion, but can beemployed in concentrations several times greater or less than that. Theratio of concentration of the thiazolocarbocyanine dye to theconcentration of pseudocyanine dye may be varied widely from 10:1 to1:10, ,for example. The most favorable conditions for supersensitlzationof the desired magnitude must be determined by experiment, the manner ofwhich will be apparent to those skilled in the art, upon a completeperusal of these specifications.

The method of incorporating dyes in emulsions are simple and well knownto those skilled in the art. In practicing my` invention, the dyes of mycombinations can be added separately or together. It is convenient toadd the dyes separately in the form of their solutions in appropriatesolvents. -The solvent must, of course, be compatible with the emulsion,substantially free from any deleterious effect on the light sensitivematerials and capable of dissolving vthe dyes. Methanol has provensatisfactory as a. solvent for vthe dyes in practicing my invention. Thedyes are advantageously incorporated in the finished, washed emulsionand should be uniformly distributed throughout the emulsion. Theemulsion can then be converted into a photographic element by coatingupon a support, such as glass, cellulose acetate, cellulose nitrateother cellulose derivative or resin, in a manner well known in the art.

The accompanying drawing is by way vof illustration and depicts thesupersensitizing effect of eight of my new combinations. Each figure ofthe drawing is a diagrammatic reproduction of three spectrograms showingfirst the sensitivity of a silver bromide emulsion containing anoxaresents the sensitivity of the same emulsion con-- taining1,1diethyl-2,2-cyanine iodide in a concentration of about 20 mg. perliter, curve C rep- .resents the sensitivity of thesame emulsioncontaining ,2,3'-diethyl-4'-methyloxathiazolocarbocyanine iodide and1,1diethyl-2,2cyanine iodide in concentrations of about 10 mg. and 2Omg. per liter, respectively. The sensitivity of the emulsion represented,by curve C, as measured through a minus blue Wratten No. 12 filter, visabout six times that of the emulsion represented by curve A.

In Fig. 2, curve D represents the sensitivity of a bromide emulsioncontaining 2,3-diethyl4'- methyloxathiazolocarbocyanine iodide in aconcentration of about 10 mg. per liter of emulsion,

curve E represents the sensitivity of the same emulsion containing3,1-diethyl-4phenyloxa zole-2cyanine iodide in a concentration of 20 mg.per liter, curve F represents the sensitivity of the same 'emulsioncontaining 2,3'diethyl4' methyl oxathiazolocarbocyanine iodide and 3,1'-diethyl-4-phenyloxazolo-2'-cyanine iodide iin concentrations of 10 mg.and 20 mg. per liter, re-

spectively. I'he sensitivity oi.' the emulsion repof the accompanyingdrawing were madein a.

wedge spectrograph. The intensity of each horizontal line Vwasapproximately 116 that at the next lower line. -Where the spectrogramswere compared, as in each of the figures of the draw-,- ing, theexposures were for the same time and test plates of each groupsweredeveloped together. l

Still further examples showing the application of my invention could becited, but the foregoing will be sufficient to teach those skilled inthe art the manner in which my invention is carried out and theprinciples of sensitizing photographic emulsions with supersensitizingcombinations such as described herein. y

What I claim as my invention and desire to se- .cure by L etters Patentof the United States is:

1. A photographic silver halide emulsion containing a supersensitizingcombination oi at least' one sensitizing oxathiazolocarbocyanin dyehaving an alkyl group on the thiazole nucleus with at least onesensitizing pseudocyanine dye selected from the group consisting of2,2'cyanine dyes, benzothia-2'cyanine dyes, selena-2'cya nine dy'es andoxazolo-2'cyanine dyes.

2. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least one sensitizingoxathiazolocarbocyanine dye having an alkyl group on the thiazolenucleus with at least one sensitizing meudocyanine dye selected from thegroup consisting of 2,2'cyanine dyes, benzothia-2'cyanine dyes,seana2'cyanine dyes and loxazolo-2'cyanine yes.

3. A photographic gelatino-.silver-halide emulsion containing asupersensitizing combination oi.' at least one sensitizingoxathiazolocarbocyanic dye having an alkyl group in the 4position withat least one sensitizing oxathiazolocarbocyanine ed from the groupconsisting of 2,2'cyanine dyes, benzothia2'cyanine dyes, Selena e2'cyanine dyes and oxazolo-f2cyanine dyes.

4. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least one sensitizingoxathiazolocarbo'cyanine dye having an alkyl group in the 4'positionwith at least one sensitizing 2,2cyanine dye.

5. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least one sensitizingoxathiazolocarbocyanine dye having an alkyl group in the 4'posi tionwith at least one sensitizing 3,4-benzothia- 2"-cyanine dye.

6. A photographic gelatino-'sllver-halide emulsion containing asupersensitizing combination vof at least one sensitizingoxathiazolocarbocyanine dye having an alkyl group in the 4"'- f dye.

position'with -at least one sensitizing oxazolo-Z'- cyanine dye.

7. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least 'one sensitizing2,3'dialkyl4'al kyloxathiazolocarbocyanine dye with at least onesensitizing 1,1dialkyl2,2"cyanine dye.

8. A photographic gelatino-silver-halide emul-v sion containing asupersensitizing combination of at least one sensitizing 2,3'dialkyl4'alkyloxathiazolocarbocyanine dye. in which the 2- and 3alkyl groups eachcontain at least two carbon atoms, with at least one sensitizing 1,1'di

alkyl-2,2- cyanine. dye in which the 1- and 1- alkyl groups each containfrom 1 to 4 carbon atoms.

; 9. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least one .sensitizing 2,3diethyl4'aikyloxathiazolocarbocyanine dye with at least one sensitizing1,1-diethyl2,2.'cyanine dye.

10. A photographic gelatino-silver-halide emul- -sion containing asupersensitizing combination of at least onesensitizing `2;3diaikyl4'a1kyloxathiazolocarbocyanine dye with at least one sensitizing2,1-diallavl-3,4benzothia2'-cyanine 11. A photographicgelatine-silver-halide emulsion containing a supersensitizingcombination of at least onesensitizing v2,3'dia1kyl4'alkyloxathiazolocarbocyanine dye, in which the 2- and 3'alkyl groupseach'contain at least two carbon atoms, with at least one sensitizing'2,1fdialkyl-3,4benzothia 2 cyanine dye in which the 2- and 1alkylgroups each contain from 1 to 4 carbon atoms. v

12. A photographic gelatino-silver-halide emulsion containing'asupersensitizing combination of at leasty one sensitizing 2,3',diethyl4alkyloxathiazolocarbocyanine -dye with at least one sensitizing 2,15'7-diethyl-SA-bcfnzothia-Z'- cyanine dye.

13. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least one sensitizing2,3'dialkyl4''al kyloxathiazolocarbocyanine dye with at least one3,1'dialkyl-4-phenyloxazolo-2-cyanine dye.

14. A photographic gelatino-silver-halide emulsion containing asupersensitizing combination of at least one sensitizing 2,3'dialkyl4'alkyloxathiazolocarbocyanine dye, in which the 2- and 3-alkyl vgroups eachcontain at least two carbon atoms. t

15. A photographic gelatino-silver-halide emulsion containing a4supersensitizing combination alkyloxathiazolocarbocyanine dye withatleast one 3,1diethylfi-phenyloxazolo-Z'-cyanine dye.

